1. Field of the Invention
This invention relates to powder coating compositions which may be cured by heat and/or high energy radiation and contain polyurethanes having (meth)acryloyl groups as binders.
2. Description of the Prior Art
Pulverulent coating compositions are known and are generally two-component coating compositions based on polyhydroxyl compounds or polycarboxyl compounds and suitable reactive polyfunctional compounds (crosslinking agents).
Crystalline, unsaturated polyester resins which can be cross-linked by means of peroxides at high temperatures have also been described (e.g. EP-A 98 655 and EP-A 188 846). These unsaturated polyester resins mixed with peroxide are not stable in storage, nor are the peroxide-containing pulverulent mixtures containing unsaturated acrylate groups described in DE-OS 2 647 700.
It is an object of the present invention to provide new powder coating binders which may be cross-linked without the addition of cross-linking components or peroxides such that they are highly stable in storage. It is an additional object of the present invention to provide powder coating binders which result in coatings which have excellent properties, in particular, hardness, solvent resistance and scratch resistance.
These objects may be achieved in accordance with the present invention by using certain selected polyurethanes having acryloyl groups as described below.